1. Field of the Invention
The present invention relates to an image processing apparatus that reads one document separately a plurality of times and combines a plurality of read images.
2. Description of the Related Art
There has been proposed an apparatus that reads one document, which is larger than a document positioning plate, a plurality of times, combines a plurality of read images, and prints the resultant. For example, Japanese Patent Application Laid-Open No. 2003-23530 discusses a technique in which an overlapped portion of the image, which is read by dividing one document, is detected, and image data pieces are combined to form one image. With this technique, even from a document, which is larger than a document positioning plate and therefore cannot originally be read, a single image representing the whole document can be acquired.
In the technique described above, there has been disclosed a technique relating to a process of determining a relative position between images, when plural images, which are obtained by reading the divided document, are combined. For example, Japanese Patent Application Laid-Open No. 2006-94237 discusses that, all pieces of the read image data are not used, but only the portion overlapped with the other image data piece is used to compare images for a positional detection. It also discusses that the entire read images are converted into a low resolution, and the images are compared by using these images. By virtue of this, the images can be compared with less quantity of information compared to the case in which the read images are compared as they are. This technique can reduce a load for the process of comparing images, resulting in that the process can be executed at high speed.
In the process of determining the relative position between images, the subject is the precision in positioning the images. For example, when the positions of the images are deviated in a document, such as a ledger sheet, having a continuous line between the divided regions, the line becomes discontinuous to thereby be noticeable. In view of this, the positioning is extremely important in the document described above. A high precision in the positioning can be expected, as the image data has high resolution.
However, in the method for reading the document as being divided as described above, the positioning is performed after the document is read. Therefore, two images have to be stored. Accordingly, there may be the case in which a sufficient storage region that stores two images having high resolution cannot be secured.